Screening for human T cell leukaemia/lymphoma virus among blood donors in Sweden: cost effectiveness analysis

British Medical Journal, May 9, 1998 by Elsa Tynell, Soren Andersson, Eva Lithander, Malin Arneborn, Jonas Blomberg, Hans Bertil Hansson, Aud Krook, Mats Nomberg, Kristina Ramstedt, Agneta Shanwell, Anders Bjorkman

One transfused patient who received plasma tested positive for the virus. This was unexpected since plasma normally contains only a few white blood cells and is often stored for a longer time than other blood components.

Cost effectiveness

An analysis of the cost effectiveness of screening should take several variables into account, such as the prevalence and incidence of infection in the population, the risks of transmission, the mortality and morbidity of those infected with the virus, and the expected survival rate of patients receiving blood components from donors infected with the virus.

The calculation of the expected seroprevalence of human T cell leukaemia/lymphoma virus types I and II in new blood donors was based on the prevalence in donors who did not come from endemic countries.[16] A more strict assessment of donors has been introduced in Sweden and potential donors from areas endemic for infection with HIV, human T cell leukaemia/ lymphoma virus, or hepatitis B are excluded from donating blood. However, an increasing number of Swedish citizens are born to immigrants from endemic areas.

The incidence of infection among already established blood donors was estimated from the prevalence in Swedes and was based on the assumption that the risk of acquiring infection mainly occurs after age 15. With an assumed mean age of blood donors of 35 years, the cumulative incidence of 1/100 000 reflects 20 years of exposure to sexual transmission for each donor. This provides a risk of seroconversion among regular donors of about one in 4 million donations; this is similar to the risk found in France.[21]

In the cost effectiveness analysis the risk of transmission from a positive donor to a recipient was assumed to be 15% for each transfusion. This was based on findings both in the retrospective study and in other published data as discussed above.[10 15 16] A risk of 30% would obviously reduce the costs by half.

We assumed that adult T cell leukaemia/lymphoma is always fatal. The incubation time from infection to the development of clinical disease and death is normally more than 30 years. Only 10% of those patients who received transfusions in our pilot study in 1992 were likely to have lived for more than 30 years after transfusion. In our analysis, the risk of developing adult T cell leukaemia/lymphoma as a result of transfusion was therefore low and even this low risk may represent an overestimate, since it is possible that the development of adult T cell leukaemia/lymphoma may be associated only with infection in childhood or infancy.[10]

Complications occurring secondary to tropical spastic paraparesis may cause premature death but no data are available to quantify this risk and we have therefore not included mortality from tropical spastic paraparesis in our analysis.

It is not feasible to selectively screen only blood donations intended for specific groups of patients, such as pregnant women and children, although this might eliminate most of the deaths caused by transmission by transfusion. It might be more practical to improve filtration so that more leucocytes were removed from all blood components intended for use in pregnant women or children; this might further decrease the risk of transmission.